This five year proposal submitted as an Early Stage Investigator R01 applies a novel mouse 3D engineered cardiac tissue model (ECT) to study the effects of mutations in the human myosin binding protein C (cMyBP-C). cMyBP-C mutations are one of the leading genetic causes of hypertrophic cardiomyopathy (HCM), a disease with a human prevalence of 1 in 500. The burden of disease spans newborn infants to older adults, and manifests with HCM, heart failure, and sudden cardiac arrest. Over 140 mutations have been identified in cMyBP-C. How these mutations affect cardiac muscle function and the development of HCM remains largely unknown. We have developed a technique to produce engineered myocardium from immature mouse cardiomyocytes deficient in murine cMyBP-C that have yet to undergo hypertrophic remodeling. Within this system we can express specific human mutant cMyBP-C, test contractile function, and define the role of applied stressors in the development of the HCM phenotype. In this proposal we will explore the main hypotheses that HCM-causing single amino acid substitutions in human cMyBP-C primarily alter contractile function, even in the absence of hypertrophy, and that mutations with severely altered contractile function demonstrate earlier and more pronounced remodeling in response to environmental stress. Experiments are proposed to pursue three principle aims: 1: Defining the functional and molecular phenotype of murine cMyBP- C deficient cardiomyocytes expressing wild-type human cMyBP-C grown in the 3D cardiac tissue model (ECT); Aim 2: Characterization of the functional impact of acute expression of human cMyBP-C missense mutations in the ECT model; and Aim 3: Identification of adaptive and maladaptive functional and molecular responses of the transgene-expressing ECT to mechanical load, electrical pacing, or adrenergic stimulation. We have selected twelve mutations in cMyBP-C that span both the age of onset from newborns to adults, and disease severity. Data derived from these experiments will extend our understanding of human cMyBP-C HCM and identify potential environmental factors that influence development of the HCM phenotype. All of the necessary reagents and techniques required in this proposal are well established within the Principle Investigators laboratory. The extensive resources and collaborative relationships at the University of Wisconsin-Madison offer an outstanding environment and enhance the likelihood of successful achievement of these aims.